public class LC_101 {
    public boolean isSymmetric(LC_144.TreeNode root) {
        if(root == null)return true;

        return isMirror(root.left, root.right);
    }
    private boolean isMirror(LC_144.TreeNode t1, LC_144.TreeNode t2){
        if(t1 == null && t2 == null)return true;
        if(t1 == null || t2 == null)return false;

        return (t1.val == t2.val) &&
                isMirror(t1.left, t2.right) &&
                isMirror(t1.right, t2.left);
    }
}
